1. Field of the Invention
The present invention relates to a golf club, and more particularly to a golf club having an improved sole portion for enhancing carry.
2. Description of the Related Art
Various golf clubs are prepared in accordance with the conditions of a course. For the tee-off, a golf club known as a driver is used to extend the carry. Since the carry directly influences the quality of the score, the position of the point of contact on the head of the golf club is an important element. The contact surface of a golf club is known as the face, and a user only ever hits a ball with the face, regardless of the playing conditions.
The center of gravity of a golf club when projected onto the face of a driver club head is usually positioned above the central portion of the face when seen from a perpendicular direction to the face. When the shape of the face is observed, it can be seen that the upper face side is wide and the lower side is narrow, thereby forming a substantial inverted trapezoid or a substantial inverted triangle, and due to this relationship, mass is inevitably offset upward. Another reason for this offset is that the part known as a hosel, into which a shaft is inserted, faces upward, thereby adding further upper mass.
Even if the position of the center of gravity is substantially 60% from the bottom surface in the height of the face, for example, this is referred to as a low center of gravity model. A contact position known as the sweet area lies in the vicinity of the center of gravity and is the area at which the greatest carry can be achieved. Hence in order to produce the greatest restitution on the head to thereby achieve carry, a ball must normally be struck on the sweet area above the central portion of the face. Depending on the conditions of the course, however, regular amateur golfers whose point of contact varies and even professional golfers may purposely shift the position of the contact point.
If a ball is struck normally against a head wind, for example, the ball is caught up in the wind and does not carry, and therefore the ball is struck at a low trajectory. In this case, the point of contact becomes the lower direction of the face. As a result, however, restitution force decreases and carry is not as great as when the ball is struck on the sweet area. Since the center of gravity is in the upper portion of the face, or in other words the sweet area which is a high restitution area is in the vicinity of the center of gravity, as described above, restitution force decreases when the point of contact deviates from this area.
Hence demands have been made for a restitution force comparable to that of the conventional sweet area in a lower position on the face portion, and various methods have been proposed to meet these demands. As a method of increasing restitution force, for example, a golf club has been disclosed (see Japanese Patent Application No. 2002-17912, for example) in which the specific surface area of the face is limited and a coefficient of restitution is set such that carry deterioration is reduced even when a ball is struck in an offset position. As a method of lowering the center of gravity in a downward direction to thereby increase restitution force in a lower position, methods such as providing a dead weight in a lower position or widening the lower direction side have been proposed (see Japanese Patent Application No. 2002-17908, for example).
As described above, techniques have been designed for increasing carry under various conditions, but none have solved the problem completely satisfactorily. There is particular scope for further improvements in restitution in a lower position removed from the sweet area. To described in more detail the aforementioned method which is implemented by limiting the specific surface area of the face and setting a coefficient of restitution, the thickness of the face portion is reduced in a specific region such that the thickness changes from the central portion to the periphery, and as a result the restitution effect is enhanced.
However, although this method is effective under specific circumstances, the restitution effect is not reliably enhanced in the lower direction of the face portion. Further, although the method of providing a dead weight is effective in itself, there are limitations on the recent trend of enlarging the head. More specifically, when the head is enlarged, a new problem arises in that the mass of the club head increases with the addition of the dead weight. The golf world by nature attaches great importance to tradition.
When the shape, mass, and so on of the head are greatly altered, a player may suffer adverse effects such as having to alter his/her swing, losing his/her rhythm, and so on. Even if an innovative club were to be developed, a long period of time would be required for the club to become established in practice. Since various difficulties are caused by greatly changing the shape of the currently established club, an ideal solution lies in the development of a golf club which is functionally improved but not greatly altered in shape from its present state, and which is therefore satisfactory to golfers.
Hence it is desirable to develop a golf club which does not differ greatly in shape from a conventional club, which is not limited in its specific functions, in which the restitution area, and particularly the lower direction thereof, can be expanded, which comprises a conventional sweet area but has improved restitution even in the lower direction, which is stable, and in which carry is increased even in head wind conditions.
The present invention has been designed on the basis of the aforementioned technical background, and achieves the following objects.